PROJECT SUMMARY/ABSTRACT In the U.S., hypertension (HTN) accounts for more cardiovascular disease (CVD)-related deaths than any other modifiable CVD risk factor, second only to cigarette smoking as a preventable cause of death for any reason. Based on recently updated clinical classifications, the US prevalence of HTN is 46%. Importantly, non- pharmacological treatment rather than antihypertensive medication is recommended for most adults who have HTN based on the new classifications (i.e., those not previously classified as HTN). Lifestyle interventions such as regular exercise are considered a first-line preventative against the development of HTN and in the treatment of diagnosed HTN. Epidemiological studies have demonstrated an inverse relationship between physical activity and physical fitness and level of blood pressure and HTN. Unfortunately, the vast majority of people are reticent to initiate exercise training and compliance in exercise training regimens that meet the minimum standards are extremely low. Additionally, some patient groups are not able to perform exercise due to a number of limitations or are not able to obtain the full benefits of exercise to reduce CVD risk. Thus, alternative non-pharmacological options to lower blood pressure and improve CVD risk are critically needed. Heat therapy, in the form of hot bath or sauna, is an ancient practice that has recently regained attention in the prevention and treatment of CVD. A recent 20+year prospective cohort study from Finland, where sauna use is extremely common and part of the culture, has demonstrated that regular sauna use was associated with reduced risk of developing HTN, which may explain in part the reduced rates of all-cause cardiovascular deaths with regular sauna use previously reported in the larger cohort. To date, there have been no clinical trials in humans to determine whether heat therapy is an effective treatment to reduce blood pressure in those with HTN. As such, we propose a clinical trial to determine whether heat therapy can effectively reduce blood pressure in HTN. We will compare the blood pressure reductions following heat therapy to standard exercise training. We hypothesize that 30 sessions of passive heat therapy using hot water immersion over 8-10 weeks will improve blood pressure in HTN individuals to a greater extent than exercise. In addition, we will evaluate clinical measures, key vascular and autonomic biomarkers of HTN, and cardiovascular health risk before and following heat therapy and exercise training. We further hypothesize that heat therapy will increase vascular compliance, lower sympathetic outflow, and improve endothelial function in individuals with HTN. Lastly, we will determine whether the acute decreases in blood pressure following a heat therapy session or exercise test will predict the sustained reduction in resting blood pressures following heat therapy treatment or exercise training in HTN subjects. These findings would provide significant predictive information beyond baseline resting blood pressures. Demonstrating that heat therapy can be used as a novel treatment for essential HTN is timely and important as there is a clear need for alternatives to exercise training and pharmacological approaches.